Adjustable high-frequency tuning unit



Jan. 24, 1961 R. J. ROWLEY ADJUSTABLE HIGH-FREQUENCY TUNING UNIT 2Sheets-Sheet 1 Filed Oct. 14. 1957 TJc Q J 2 i. iPiiL FIE E IIVVf/VTORRoss/2r J. Rovrurv By Arron/wry Jan. 24, 1961 R. .1. ROWLEY 2,969,460

ADJUSTABLE HIGH-FREQUENCY TUNING UNIT Filed Oct. 14, 1957 2 Sheets-Sheet2 FREQUENCY, m c

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INVENTOR ROBERT J. Rowusy ATTORNEY United States Patent ADJUSTABLEHIGH-FREQUENCY TUNING UNIT Robert J. Rowley, Cedar Rapids, Iowa,assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation ofIowa Filed Oct. 14, 1957, Ser. No. 690,164

4 Claims. (Cl. 250-40) This invention relates generally to adjustablehigh-frequency tuning units of the inductance-capacitance type and moreparticularly to an adjustable tuner for use in the ultra-high-frequencyspectrum.

In the design of tuning units for use in the ultra-highfrequency bandsuch as in the range of 235250 megacycles, difiiculties are encounteredsince this portion of the spectrum lies at the lower end of the coaxialline or cavity type tuner range wherein inductive and capacitive effectsare distributed and at the upper end of the frequency range whereinlumped constant inductance and capacitance parameters may be employed.At these high frequencies a design approach based on lumped constantsbecomes extremely critical in that lead lengths and spacing of theparameters becomes impractical and in many cases prohibitive. On theother hand, the use of a cavity or shorted coaxial line for use in thisfrequency range necessitates generally a greater size requirement thanis ordinarily tolerated in present-day electronics whereinminiaturization and compactness is desired.

it is an object, therefore, of this invention to provide an adjustabletuning unit for use in the ultra-high-frequency range which, by itsconstruction, contains minimum stray inductance, provides eflicientshielding of electromagnetic fields contained within the device, iscontinuously adjustable over a desired frequency range, and provides inone small unit a fixed shunting capacitor, a coupling capacitor, and aby-pass capacitor in conjunction with a variable inductance.

The tuner to be described may be considered as an adjustable coil,fixed-capacitor, shunted circuit with a lowimpedance end of the coilused as a grounded shield. It might also be considered as a shortedcoaxial line with the outer conductor compressed and the inner conductorretaining its original length but being formed in a spiral shape.

A feature of this invention consists of the provision of two coaxialconductive cylinder members insulated from one another with a coilcontained within and means provided to vary the effective length of thecoil while maintaining the necessary fixed capacitive effects.

The manner in which the tuner incorporates the advantages of effectiveelectromagnetic field shielding, a high quality factor, and minimumcoupling and by-pass inductance may be realized by the following,description when read in view of the accompanying drawingsin which:

Figure 1 is a schematic diagram of the frequency-determining parameters;

Figure 2 is a sectional view of the physical construction of oneembodiment of this invention;

Figure 3 is an exploded isometric of the embodiment of Figure 2;

Figure 4 is a graphical representation of typical operatingcharacteristics;

Figure 5 is a sectional view of a second physical embodiment of thisinvention; and

Figure 6 illustrates a portion of an adjusting tool to be used inconjunction with the embodiment of Figure 5.

With reference to Figure 5, an insulated core member 19 is seen to havewound thereon a silver-plated wire 11. A metallic sleeve 12; is pressedon to the reduced diameter end of core member 10. Sleeve 12 and wire 11are electrically connected by soldering or other means at a point 13 onsleeve 12, the point 13 being a projecting tab-like portion on sleeve12. The assembly of core member 10 and sleeve 12 is pressed into ametallic cylinder 1 A capacitive effect is realized between metallicsleeve 12 and cylinder 14 since from Figure 5 it is to be noticed thatsleeve 12 is smaller in diameter than the inside diameter of cylinder14. This capacitance, with reference to Figure 1, is illustrated ascapacitance B and is the main shunt capacitance of the tuner.

A terminal lug 16 is pressed into a recess in insulating core member 169and is thus held in close proximity to the sleeve member 12. A secondcapacitance is then realized between terminal lug 16 and sleeve member12 and this capacitance acts as a coupling capacitor illustrated inFigure l as capacitance C.

With reference once again to Figure 5, an insulating dielectric sleeve18 is formed about inner cylinder 14 and a second cylindrical metallicmember 17 surrounds in sulating sleeve 18. A third capacitance is,therefore, realized between outer metallic cylindrical member 17 andinner metallic cylinder 14, the insulating sleeve 18 acting as adielectric therebetween. This capacitance, with reference to Figure l,is illustrated as capacitor A and functions as a b y-pass capacitorbetween the low-impcdance end of the tank circuit and ground. The groundsymbol in Figure 1 represents the grounding of outer cylindrical member1'7 when the tuner is connected into a chassis. With reference then toFigures 1 and 5, a terminal 15 on inner cylinder 14 is by-passed toground by the capacitor A and this terminal 15 would serve as the B+connector when the tuner is employed in a circuit. Like referencenumerals in Figures 1 and 5 indicate the correlation between thephysical construction of elements and the schematic representationthereof. Thus terminal 12, the input terminal to the tuner, is theconnection to the high-impedance end of coil 11. Terminal 16 is theoutput terminal of the tuner taken from coupling capacitor C which, aspreviously described, is the capacitance realized between terminal lug16 and cylindrical sleeve 12. Terminal 15, in being connected to theinner metallic cylinder, functions as the 13+ connector and is by-passcdto ground through the physical connection of outer metallic cylinder 17and a chassis into which the tuner would be installed.

Referring again to Figure 5, a sliding spring contact 19 is seen to forma connection between a point on inductive wire 11 and the inner surfaceof metallic cylinder 14. Slide contact 19 makes connection withinductive wire 11 at the point indicated by reference numeral 25 and itis seen that in Figure 1 the schematic representation is that of slidingcontact 25 on coil 11.

Member 15 is formed such that it is spring loaded between a point oninductive wire 11 and the inner surface of cylinder 14. Tuning isthereby accomplished by the insertion of an adjustable tool such asindicated in Figure 6 whereby the tool is inserted within cylinder 14and sliding contact 19 is engaged in slot 33 of the tool 32 wherebyrotation of the tool 32 will cause member 1? to advance along coil 11and reduce its effective length while maintaining continuous connectionbetween the contacted portion of coil 11 and the inner surface ofcylinder 14.

The operation of the tuner may then be summed up in the followingmanner. The junction of the silver wire 11 and metallic sleeve 12comprises the high-impedance 3 end of the tuner while the connectionbetween wire 11 and inner cylinder 14 as maintained by sliding contact19 comprises the low-impedance end of the tuner. Inner cylinder 14,while it is at 13+ potential, is essentially at ground potential toradio-frequency voltage due to the by-pass capacitor A which surroundsthis unit. Ey-pass capacitor A, as previously described, is thecapacitance realized between inner cylinder 14 and outer cylinder 17.Because the outer cylinder 17, which forms one plate of capacitance A,is soldered or otherwise electrically connected to a chassis, unwantedcapacitor inductance is held to an absolute minimum.

The shunting capacitor, capacitor B in Figure l, is the fixedcapacitance between metallic sleeve 12 and inner cylinder 14 formedbetween the low-impedance point (inner cylinder 14) and thehigh-impedance point (metallic sleeve 12). In an embodiment tested, thecapacitance B had a value of approximately five micromicrofarads, thecapacitor A was larger than 500 micromicrofarads and the capacitor C hada value of approximately one micromicrofarad. The small capacitor C isthus properly coupled to the high-impedance end of the tuner.

Figure 4 represents the frequency of the unit as a function of thenumber of rotational turns of sliding contact 19 from maximum inductanceand the quality factor (Q) as a function of the frequency with the unitbeing shunted by external capacitors of various values. This externalshunting capacitor is indicated as capacitor 36 between input terminal12 and ground in Figure 1. As indicated in Figure 4, a substantiallylinear increase in frequency is realized between 225 and 250 megacyclesas the sliding contact 19 is turned from maximum inductance. A high andsubstantially constant Q reading is seen to be realized throughout therange.

A preferred embodiment of the invention is illustrated in Figures 2 and3. This embodiment operates on the identical principle of thatillustrated in Figure 5 but includes a novel inductor construction andsliding contact means whereby adjustment may be made by means of a screwdriver adjustment, thus requiring no special tool.

The embodiment of Figure 2 is shown in cross section excepting theinductance core element. Figure 3 represents an exploded isometric viewof the embodiment of Figure 2. As in the construction previouslydescribed of the embodiment of Figure 5, the tuner of Figure 2 onceagain is seen to be comprised of an inner cylinder 14 and an outercylinder 17 having an insulating dielectric sleeve 18 therebetween.Insulating core member is pressed within the confines of inner cylinder14 and has pressed thereon a metallic ring member 12 of smaller diameterthan that of inner cylinder 14 such that capacitance B of Figure 1 isonce again realized between metallic sleeve 12 and inner cylinder 14. Inthis embodiment, the inductive wire member differs in that insulatingcore member 10 is machined with a fiat-threaded groove in which is wounda fiat silver ribbon Wire 11. As indicated in Figure 2, thehigh-impedance end of the inductive wire 11 is once again electricallyconnected to a terminal portion of metallic sleeve member 12 at a pointindicated by reference numeral 13. A terminal lug 16 is seen to bepressed into the core member 10, and, due to its proximity with metallicsleeve 12, a capacitance corresponding to capacitance C in Figure 1 isrealized between terminal lug 16 and metallic sleeve 12. Outer metalliccylinder 17 once again functions as the lower plate of a by-passcapacitor to ground indicated as capacitance A in Figure 1.

In this embodiment, adjustable contact 19 which forms the continuouselectrical connection between inner cylinder 14 and inductive wire 11 ismade to rotate in the threaded groove of core member 10. With referenceto Figure 3 an insulated sleeve member 22 cooperates with slidingcontact 19 and facilitates tuning by means of a screw driver slot 34.Without this insulated sleeve member 22, which functions as an adapter,a special tuning tool would be required. With reference to Fig ure 3insulating sleeve member 22 is seen to be formed of a hollow cylindricalmember comprising end portions 23 and 24 and a center portion 26 ofreduced diameter. Center portion 26 is formed with diametrically opposedslotted portions 27 and 28. Slide contact 19 is seen to be formed of aspring-like material such that two ends may be crimped over' to form aslidable positioning means along slot 27 on center portion 26 of sleeve22. A tab-like portion 25 extends inwardly from the member 19 andfunctions as a spring-loaded contact with metallic wire 11 when sleeve22 and contact 19 are placed over insulating core member 10. It is thusseen that rotation of sleeve member 22, with respect to insulating coremember 10, forces sliding contact member 25 to travel along the grooveswithin which inductive wire 11 is wound. With reference to Figure 2 acon tinuous contact is thus maintained by tab portion 25 on inductivewire 11 while the outer surface of sliding contact member 19 maintains asliding spring-loaded contact against the inner surface of cylinder 14.This construction, therefore, eliminates the need for a special tool andcompletely encloses the low-impedance end of the tuner. Adjustment maybe made by insertion of a screw driver in slot 34 of sleeve member 22.

The embodiment of Figure 2 is additionally provided with an insulatorcap 31 which presses over inner cylinder 14 to hold adjusting sleevemember 22 within the confines of the tuner. Cap 31 additionally acts asan insulation ring and may be seated in a hole in a receiver chassis andeffect the necessary insulation between inner cylinder 14 and thechassis, inner cylinder 14 being at 13+ potential.

It is to be noted that in either of the above discussed embodiments thetuner of this invention provides an almost complete shielding fromelectromagnetic field radiation. Since the one end of the tuner which isleft open for tuning purposes and is not metallically shielded in thelow-impedance point of the tuner, very little electromagnetic fieldradiation from the tuner is possible. Fillther, and more particularlyregarding the embodiment of Figure 2, it is seen that inner metalliccylinder 14 extends substantially beyond the low-impedance end of coil11 and thus provides additional shielding.

The tuner of this invention provides an extremely compact unit and byits construction lends itself to incorporation in air-cooled modulechassis construction. An aircooled chassis may be air-tight inconstruction while incorporating one of the tuners of this invention andstill be tunable from outside the module.

Further, the physical shape of the tuner of this invention is ideal foruse with subminiature tubes in that the length and diameter arecomparable to that of a shielded tube.

Although this invention has been described with respect to particularembodiments thereof, it is not to be so limited as changes andmodifications may be made therein which are within the full intendedscope of the invention as defined by the appended claims.

What is claimed is:

1. An adjustable high-frequency tuning unit of the variable inductancetype comprising, an insulating core member with an inductive memberwound on a first reduced diameter portion thereof, a conductive sleevemember placed over a second reduced diameter portion of said coremember, one end of said inductive member electrically connected to saidsleeve member, a first external conductor connected to said sleevemember, a hollow conductive cylinder, said core member contained withinsaid conductive cylinder, an outer conductive surface surrounding saidconductive cylinder and dielectrically separated therefrom, a conductiverod-like member inserted in said core member in juxtaposed andspaceseparated relationship with said conductive sleeve member, a secondexternal connector connected to said rodlike member, a third externalconnector connected to said conductive cylinder, and adjustable shortingmeans between said wire turns on said core member and said conductivecylinder.

2. A capacitive-inductive tuner comprising, an insulated cylindricalcore member having first and second end sections of reduced diameter, aninductive member wound on the first end section, a conductive sleevemounted concentrically about the second end section, one end of saidinductive member extending through said core member and electricallyconnected to said conductive sleeve, a first conductive cylindricalmember, said core member secured within said first cylindrical member, aconductive lug member received in said second end section of said coremember, said lug member radially displaced from the longitudinal axis ofsaid core member and in spacial proximity with the inner surface of saidconductive sleeve, a second conductive cylindrical member surroundingsaid first cylindrical member and dielectrically insulated therefrom,first, second and third terminals connected respectively to said firstcylindrical member, said conductive lug member and said conductivesleeve, and a spring contact member maintaining electrical connectionbetween said inductive member and said first cylindrical member, saidspring contact member being positionable along said inductive member tovary the effective inductive length thereof.

3. An adjustable high-frequency tuning unit of the variable inductancetype comprising, an insulating core member formed with a spiral groovetherein, an inductive member wound about said core and recessed in saidspiral groove, a conductive sleeve placed over a reduced diameter endportion of said core member, one end of said inductive memberelectrically connected to said sleeve member, a first external conductorconnected to said sleeve, a hollow conductive cylinder, said core membercontained within said conductive cylinder, an outer conductive surfacesurrounding said conductive cylinder and dielectrically separatedtherefrom, a conductive rod-like member inserted in said core member injuxtaposed and space-separated relationship with said conductive sleeve,a second external connector connected to said rod-like member, a thirdexternal connector connected to said hollow conductive cylinder, aninsulating adapter sleeve rotatably mounted about said core member, acontact member atfixed to said adapter sleeve, said contact membernon-rotatably supported by and slidably positionable with respect tosaid adapter sleeve whereby rotation of said adapter sleeve effectsrotation of said contact member along the spiral grooves in said coremember, and said contact member being formed to maintain a continuouselectrical connection between said inductive member and the innersurface of said conductive cylinder to vary the effective length of saidinductive member.

4. An adjustable high-frequency tuning unit of the variable inductancetype comprising, an insulating core member formed with a spiral groovetherein, an inductive member wound about said core and recessed in saidspiral groove, a conductive sleeve placed over a reduced diameter endportion of said core member, one end of said inductive memberelectrically connected to said sleeve, a first external connectorconnected to said sleeve, a hollow conductive cylinder, said core membercontained within said conductive cylinder, an outer conductive surfacesurrounding said conductive cylinder and dielectrically separatedtherefrom, a conductive rod-like member inserted in said core member injuxtaposed and spaceseparated relationship with said conductive sleeve,a second external connector connected to said rod-like member, a thirdexternal connector connected to said conductive cylinder, an insulatingadapter sleeve member having a longitudinally extending through-slottherein, said adapter mounted concentrically about and rotatable withrespect to the grooved portion of said core member, a spring contactmember mounted concentrically about said adapter, said contact memberbeing non-rotatable with respect to said adapter sleeve andlongitudinally slid able with respect thereto, a spring tab formedinwardly from said contact member and passed through said through-slotand into engagement with a point on said inductive member, said contactmember being adapted to be in spring-loaded slidable engagement with theinner surface of said hollow conductive cylinder, whereby rotation ofsaid adapter sleeve member causes the contact member to rotate along thespiral grooves on said insulating core member and be displaced alongsaid adapter to effect a continuous electrical contact between the innersurface of said conductive cylinder and said inductive member.

References Cited in the file of this patent UNITED STATES PATENTS1,942,751 Evans Jan. 9, 1934 1,986,805 Gebhard et a1. Jan. 8, 19352,691,096 Starner et al. Oct. 5, 1954

